need help from Mopar guru's

[Ken Haase]

Got a friend who is close to having his 511" B block ready to go in the car. The pistons are averaging .010" above the deck. He's using .040" Cometic gaskets, and that's a little less quench than he would prefer. The valve to piston is over .100" on both intake and exhaust. But what is troubling him is a local Mopar expert told him "don't run it(or even start it) it'll blow up". Is there something here we're not cognizant of?

The 451" he replaced had the same above deck number and .040" gasket with many seasons of trouble-free service. Any and all advice, tips, etc. will be much appreciated.

Thanks

[bigfoot584]

I must be missing something other than your Mopar man
dose not know what he's talking about.

Paragraph two answered paragraph one, 60 cubic inch
means nothing, valve clearance is safe.

my .02

[Todd Gross]

I'm seeing that you have a piston that's .010" AB and a .040" head gasket. That equates to a piston to head clearance of .030"
That's tight for a small block, let alone a big block.
What do you have for Connecting Rods? Steel or Aluminum?
Same for Block. Cast Iron of Aluminum? The growth coefficients will affect things, but .030" on a big Block is too tight in my opinion.

[Steve Stasko]

It may not blow up, but it will definitely pop head gaskets every 3-4 weeks. Usually at the dowel pin on the front of the block.


Cometic makes a thicker gasket for that application, I think it's .066 thick. That's the gasket you need to make it live (in addition to a girdle, good main caps, and probably some hard block if it's a factory block).

[Ken Haase]

Guys, thanks for the replies so far. My experience is with other brands so I have no first hand experience with B/RB Mopars. Bigfoot, my initial reaction was along the lines of your thoughts.
JMan, and Steve, he's using good H-beam steel rods and 4340 stroker crank in an OEM 400 block with a girdle, but it's not filled. I'm somewhat familiar with the co-efficient of linear expansion for different metals, and these clearances would not be a problem in my limited experience.
If I'm understanding this correctly, this issue is related to a lack of sufficient block rigidity? With 17 head bolts, I'm a little surprised that there would be a gasket clampling problem. And, I'm still unclear how there was not a problem with the 451". He's using the same block and it had no girdle at that time. But it was 10.5 instead of 12.5 CR.
I will suggest he think about the thicker gasket. Thanks again.

[ss3011]

My 455 stocker Pontiac has a 0 deck and a .030" head gasket . It runs to 6200 rpm and usually imprints the piston numbers on the quench area of the combustion chamber . Bottom line is you need more than .030" , especially if the rpm is higher .

[Everett Vassar]

Cometic will make any thickness you want. I'm thinking .042 clearance is what you would shoot for maybe .038 we had this problem on a 440 years ago. We had the block decked for the old TRW dome pistons not knowing they had changed the pin loc

[Everett Vassar]

Cometic will make any thickness you want. I'm thinking .042 clearance is what you would shoot for maybe .038 we had this problem on a 440 years ago. We had the block decked for the old TRW dome pistons not knowing they had changed the pin loc at some point. Wound up with a nice set of Ross pistons still out of the hole, we had to order Cometics about .065 thick. We had no head gasket issues,but the pushrods would not stay in it. We didn't run that motor very long, just looking back and wondering if raising the head off the block that far was making the push rods too short?

[Ken Haase]

He's going with .051 Cometics. Thanks to all for the help, and especially to a long-time former Mopar S/S'er for the initial warning. Saved my friend a lot of grief and $'s.